With manufactured products which are cut out by plasma cutting, laser cutting, gas cutting, or some other cutting method, in order to enhance the product quality of welding which is to be performed subsequently or to attain some other objective, it is not uncommon also to require a beveling or chamfering process (both of which will subsequently be termed “beveling”) to be performed upon the cut surface at the outer surface of these manufactured products. For example, in the case of manufactured products which are to be used as components for the body or the frame of a construction machine, beveling is requested in about 70% of cases. Although beveling may be divided into many different types according to the shape of the processed surface, according to many of these types of beveling, the surface which has been beveled consists of a combination of two cut surfaces whose angles with respect to the main surface of the manufactured product are different. This type of beveling is implemented via two cutting sub-process stages, in order to form each of these two cut surfaces. In the first cutting sub-process stage cutting may be performed upon the base material, for example, in the direction perpendicular to the main surface of the base material, and thus the manufactured product is cut out from this base material. Then, in the second cutting sub-process stage, bevel cutting is performed upon the external shape of this manufactured product which has been cut out in, for example, a direction which is inclined with respect to the main surface of the manufactured product, and thereby a portion of its outer edge is cut away.
With respect to beveling, certain inventions are known from U.S. Pat. No. 6,326,588 and Japanese Laid-Open Patent Publication Heisei 11-57999.
In U.S. Pat. No. 6,326,588, a method is disclosed of performing cutting for beveling in two stages. With this method, first, a manufactured product is cut out by cutting the base material vertically with a laser beam; thereafter the scrap is removed, leaving only the manufactured product; thereafter, the position of the external shape of the manufactured product is detected, and this position of the external shape which has been detected is supplied to a laser control unit; and, finally, the outer edge of the manufactured product is cut away at an angle using an inclined laser beam.
And, in Japanese Laid-Open Patent Publication Heisei 11-57999, a beveling cutting device of the following type is disclosed. That is, with this beveling cutting device, a manufactured product which has been cut out beforehand is received and is placed in a predetermined position, and the positions of a plurality of spots upon the external shape of this manufactured product are detected by using a laser sensor or the like. Based upon these positions of the plurality of spots upon the external shape which have thus been detected, the external outline of this manufactured product is perfectly defined as a union of straight lines, circles, circular arcs, or the like, and geometrical shape data are generated. The external shape of the manufactured product is then cut at an inclined angle by using this geometric shape data.
Furthermore, although this has no direct relevance to beveling, in Japanese Laid-Open Patent Publication 2003-251464, a method is disclosed for accurately determining cutting positions when cutting out manufactured products from a base material. Here, two types of method are disclosed. With the first method, the base material is photographed with a camera, the coordinates of the contour line of the base material are calculated from the image which has been photographed, and drawings of the products to be manufactured are nested within the region which can be cut, inside this contour line of the base material which has thus been calculated. And, with the second method, data is stored in advance for the size and shape of the base material, and for the size and the shape of the drawing which is to be cut out therefrom, a plurality of spots upon the base material are photographed, the contour line of the base material is calculated with these spots which have been photographed, this contour line and the data for the base material which is stored in advance are compared together, the positional deviations between these data sets are matched, and thereafter cutting out of the manufactured products is performed.
In order to enhance the working efficiency of the beveling, it is desirable to make it possible to perform the above described two or more cutting sub-process stages continuously, using a single cutting device whose cutting position can be automatically controlled by numeric control (NC). However although, in the first cutting sub-process stage, it is possible to perform the processing at a high accuracy in which the performance of NC is reflected, in the second and subsequent cutting sub-process stages, the problem arises that the accuracy of the cutting is undesirably deteriorated. The reason for this is that, when in the first stage the manufactured product has been separated from the base material, the manufactured product may move since it has lost its support from the base material, so that the relative position of the manufactured product with respect to the cutting device may deviate slightly from its original position, which is undesirable.
U.S. Pat. No. 6,326,588 and Japanese Laid-Open Patent Publication Heisei 11-57999 provide a method for performing sensing of the position of the external shape of the manufactured product, and for calculating the external outline of the manufactured product from the result of this sensing.
However, in order to calculate the external outline of the manufactured product accurately, it is necessary to sense the positions of a large number of points upon the external outline of the manufactured product. And, in order to calculate the geometric shape data which perfectly defines the external shape of the manufactured product from these detection results, it is necessary to perform a large amount of calculation processing. Furthermore, when detecting the position of the external shape of the manufactured product, it is necessary either to remove the scrap and leave only the manufactured product, as in U.S. Pat. No. 6,326,588, or to extract only the manufactured product, as in Japanese Laid-Open Patent Publication Heisei 11-57999, and to mount it upon the cutting device. Since these operations are necessary, it is inevitable that quite a long waiting time period is required between the first cutting sub-process stage and the next cutting sub-process stage, and accordingly it is difficult to make these two cutting sub-process stages succeed one another continuously in an efficient manner.
Furthermore in Japanese Laid-Open Patent Publication 2003-251464 (although this is a method for calculating the external outline of the base material, not that of the manufactured product), a method is disclosed of photographing a number of spots upon the base material with a camera and calculating contour line data of this plurality of spots, and of matching positional deviation between this contour line data of the plurality of spots, and external shape data which is stored in advance. In order to implement this method, it is necessary to discover which portion of the external shape data which is stored in advance corresponds to the contour line at the plurality of spots which have been obtained from the photographic image. However, no method for doing so is disclosed in Japanese Laid-Open Patent Publication 2003-251464. Moreover, there is no problem of scrap when calculating the external outline of the base material as in Japanese Laid-Open Patent Publication 2003-251464. By contrast, when calculating the position of the external shape of a manufactured product which has been cut out from a base material, it is necessary to eliminate any possibility of mistakenly detecting the scrap which is present around the manufactured product, as being the manufactured product.